1. Field of the Invention
The present invention relates to a mechanism for steering the front and rear wheels of a four-wheel-steerable vehicle.
2. Description of the Relevant Art
There are known four-wheel-steerable (4WS) vehicles having a front wheel steering device operatively coupled to a steering wheel and a rear wheel steering device mechanically connected to the front wheel steering device to improve cornering capability. The four-wheel-steerable vehicles however require, of necessity, a greater steering effort than front-wheel-steerable (2WS) vehicles in which only front wheels are turned.
Japanese Laid-Open Patent Publication Nos. 59-70259 and 59-70260 both published Apr. 20, 1984, and Japanese Laid-Open Patent Publications Nos. 61-181776 and 61-181777 both published Aug. 14, 1986 disclose front and rear wheel steering systems in which one or both of front and rear wheel steering devices in a 4WS vehicle have a mechanical variable-gear-ratio mechanism for improving vehicle maneuverability and reducing a steering force required.
Where a gear ratio is selected for greater vehicle maneuverability, the steering force required is large and tends to vary to a large extent. On the other hand, where a gear ratio for a reduced steering force is established, the vehicle maneuverability is apt to be lowered. Actually, therefore, a gear ratio should be determined on a compromise between improved vehicle maneuverability and reduced steering forces required. Not much freedom has been available for selecting gear ratios.